Author: blass uri
Date: 12:16:02 07/31/99
Go up one level in this thread
On July 31, 1999 at 12:55:54, Robert Hyatt wrote: >On July 31, 1999 at 12:34:34, Robert Hyatt wrote: > >>On July 31, 1999 at 03:08:42, Ed Schröder wrote: >> >>>>This is easy to test. >>>> >>>>My hypothesis: simple search is not good enough to discover that all moves >>>>but one lead to mate, in any positions except for those near the point where a >>>>game is already over (one side is mating the other). >>>> >>>>Ed's: A simple search is good enough to discern forcing moves. >>>> >>>>How about someone looking for positions where all moves but one lead to a >>>>forced mate... IE one move must _not_ get mated, while all the rest do. >>>>Then we decide whether the short search of Rebel can see this or not. >>>> >>>>Then we decide how often this kind of position occurs, and how often (when it >>>>does) is a shallow search enough to recognize the forced nature. >>>> >>>>I don't think (a) it will work very well; (b) that it is worth the effort to >>>>search with alpha=-inf, beta=+inf for every root move; (c) that by the time >>>>this might have a chance of identifying a forcing move, the game is already >>>>over and saving time is pointless... >>>> >>>>My opinion, of course... >>> >>>How about going one step further. Some years ago I did an experiment. >>>Search the first iteration without A/B, then: >>> >>>if (best_score - second_best_score > margin_one) limit time control. >>>if (best_score - second_best_score > margin_two) limit time control even more. >>> >>>etc. >>> >>>Also I tried this for the second iteration as well. Results were not bad at all >>>as it also catches forced moves that aren't recaptures and escapes from >>>checks. Moves sequences like 1..g5 2.Bg3 were also discovered and >>>2.Bg3 was played very fast. I also remember a case 1.a7 Ra8 preventing >>>the pawn to promote. Since 1..Ra8 was the only move 1..Ra8 was played >>>instantly. >>> >> >> >>that's an easy one to break. Take the position Cray Blitz vs Belle (I will >>try to find the FEN but it is in one of the test suites (Bxh6 is a draw, Qxb6 >>loses). >> >>I'll bet you that you discover that Qxb6 is +3 better than any other move with >>a 1 ply search. And a 2 ply search... and a 3, 4, 5 and 6 ply search... and >>beyond... until you finally see that it loses badly. >> >>Using your approach will get you killed there. Care to guess how I know? I >>was there. I used a scheme almost exactly like yours in 1980 or so, and it >>made that very same mistake in that very same game, and lost quickly... A 2 >>minute search would have shown Bxh6 drew and Qxb6 lost. But CB assumed that >>"Qxb6 was 'easy'" >> >> >> >> >>>Note that Q-search in Rebel's first and second iteration were limited to 6 and >>>8 plies to prevent the search to explode when A/B is not active. I also do >>>check extensions in Q-search to discover mates which catches the most >>>important ones but not all of course. >>> >>>Ed Schroder > > >Here is the position: > >5r1k/6p/1n2Q2p/4p//7P/PP4PK/R1B1q/ w > >the position in ascii: > > +---+---+---+---+---+---+---+---+ > 8 | | | | | | *R| | *K| > +---+---+---+---+---+---+---+---+ > 7 | | | | | | | *P| | > +---+---+---+---+---+---+---+---+ > 6 | | *N| | | Q | | | *P| > +---+---+---+---+---+---+---+---+ > 5 | | | | | *P| | | | > +---+---+---+---+---+---+---+---+ > 4 | | | | | | | | | > +---+---+---+---+---+---+---+---+ > 3 | | | | | | | | P | > +---+---+---+---+---+---+---+---+ > 2 | P | P | | | | | P | K | > +---+---+---+---+---+---+---+---+ > 1 | R | | B | | *Q| | | | > +---+---+---+---+---+---+---+---+ > a b c d e f g h > > >and my search results (PII/300 notebook): > >(early iterations like Qxb6 a lot, scores over +4.) > 8 8.27 0.26 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. b4 e3 > 8-> 9.56 0.26 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. b4 e3 > 9 10.54 0.57 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. b4 e3 6. b5 > 9-> 12.16 0.57 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. b4 e3 6. b5 > 10 13.17 -- 1. Qxb6 > 10 43.47 0.00 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. Kg3 Qe1+ 6. Kh2 Qf1 > 10-> 51.88 0.00 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. Kg3 Qe1+ 6. Kh2 Qf1 > 11 54.47 -- 1. Qxb6 > 11 1:47 -2.58 1. Qxb6 Rf1 2. Qd8+ Kh7 3. Qd3+ e4 > 4. Qxf1 Qxf1 5. a4 e3 6. Ra2 Qxc1 7. > b4 Kg6 > 11 2:12 0.00 1. Bxh6 Qxa1 2. Qxe5 Rf6 3. Bg5 Rf2 > 4. Qe8+ Kh7 5. Qh5+ Kg8 6. Qe8+ Kh7 > >As I mentioned, this is from Cray Blitz vs Belle, 1981 ACM NACC tournament. > >Bob I looked in this position and the latest version of Junior can find Bxh6 even at depthes 8 or 9 (eqvivalent to brute force depth of 4,5) It can find Bxh6 even at level 1 second per move on pentium200. I think that Cray blitz and crafty has problem in this position relative to part of the commercial programs. Uri
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.